The present invention relates to location, maps, and/or navigation and, more particularly, to location tracking method(s) and system(s).
Signal strength may be used to determine the location of a device throughout an intended coverage area. Conventional systems require a calibration phase, in which the device is systematically positioned at various points throughout the radio space in order to capture a set of signal strength samples for signals transmitted within range. After signal strength samples have been captured at all the desired calibration points, software may build a “radio map” of the coverage area. The radio map may include signal strength probability densities throughout the coverage area. Once the calibration phase is complete, the device or other user devices report signal strength values to the system, which predicts the location of the device by comparing the reported values in the radio map.
However, the calibration phase is time-consuming, and obstacles in the coverage area that alter signals disrupt the results. One common obstacle is human bodies, which may be modeled as large sacks of fluid that absorb energy. Human bodies are likely less prevalent in the calibration phase than when the system is implemented, which leads to inaccuracies. Further, the results may be unreliable because any object moved from calibration phase locations can significantly alter the radio map. In outdoor environments, seasonal changes such as leaves on trees or shrubs in warmer months impact the radio map. In indoor environments, changing inventory on store shelves, moved kiosks, or nearby people impact the radio map.
In addition, the various brands and technologies of user devices sense and report signal strengths in different ways. For example, the wide variety of antenna configurations used in the wireless industry results in different signal strength values, which also may be measured using varying signal strength units. Empirical tests have shown determining the current location of a device of brand X when the radio space has been calibrated for a device of brand Y is difficult and universal mapping algorithms to account for the differences among device types may not be feasible.